Problems Recording and Playing Back Audio Simultaneously

Question

I'm having some trouble working with the iOS Audio frameworks to create a simple app. I would like to record audio through the Microphone and play it back to the user while recording.

I have tried each of the audio framework layers(AVFoundation, Audio Queue API, and RemoteIO), but have only found old documentation and broken examples.It seems like a simple request that AVFoundation should handle, but I have explored the following other SO questions and still find myself circling for hours to get the hang of this. Here is what I have reviewed:

• iOS: Sample code for simultaneous record and playback (Other SO Users also state the accepted answer is not concrete and difficult to implement even with a delay of ~70ms.)
• Record and play audio Simultaneously (From 2010 and very high level, I have downloaded the sample code and can't find a working example that does simultaneous playback and recording).
• Adjust the length of an AudioUnit Buffer (RemoteIO is so confusing to me right now, is this really required?)

I have also downloaded and reviewed both the SpeakHere and AurioTouch sample projects from Apple. I promise I wouldn't post up without hours of googling and struggling. You can see "record audio and playback iOS simultaneously" returns many dated and non-working examples.I know myself and the community could really benefit from some updated documentation and examples in the audio section. RemoteIO seems to be too advanced for such a simple task. Thanks again for your help and consideration.

Answer 1

The appropriate way to do this is via AudioUnit APIs, even though it seems like a common scenario which should be handled by higher level APIs.

I wrote a small demo app using AudioUnit. You're free to try it our and modify it for suiting your purpose. The demo app does record audio and play it simultaneously, but it's recommended to use a ear phone to see the effect.

Answer 2

The RemoteIO Audio Unit is the only way to play back what is being recorded with low latency. RemoteIO is low latency because it runs audio callbacks in a separate dedicated real-time thread which is why it is fast, but also why it is a bit more complex to code. All the other iOS audio APIs are built on top of RemoteIO and thus add latency.

You will also need to configure the app's Audio Session APIs to request low latency with the appropriate audio session type. The foreground app can request and get audio input and output latencies as low as 5.6 milliseconds on most iOS devices most of the time.